A conveyor oven is an oven with a conveyor that moves through a heated tunnel in the oven. Conveyor ovens are widely used for baking food items, especially pizzas, and the like. Examples of such ovens are shown, for example, in U.S. Pat. Nos. 5,277,105, 6,481,433 and 6,655,373.
Conveyor ovens are typically large metallic housings with a heated tunnel extending through them and a conveyor running through the tunnel. Usually such conveyor ovens are either 70 inches or 55 inches long, although they may be constructed in any suitable size. The conveyor (in the form, e.g., of a conveyor belt) transports food items through the heated oven tunnel at a speed calculated to properly bake food on the conveyor belt during the time the conveyor carries the food through the oven. The conveyor ovens include a heat delivery system including blowers which supply heat to the tunnel from a plenum through passageways leading to metal fingers opening into the oven tunnel, at locations above and below the conveyor. The metal fingers act as airflow channels that deliver streams of hot air which impinge upon the surfaces of the food items passing through the tunnel on the conveyor. In modern conveyor ovens, a microprocessor-driven control may be employed to enable the user to regulate the heat, the speed of the conveyor, or other parameters to properly bake the food item being transported through the oven.
The conveyor generally travels at a speed calculated to properly bake food items on the belt during the time period required for the conveyor to carry them through the entire length of the oven tunnel. Other food items requiring less time to bake may be placed on the conveyor at a point part way through the oven so that they travel only a portion of the length of the tunnel. A pizza is an example of a product which might require the full amount of baking time in order to be completely baked in the oven. A sandwich is an example of a product which might require only a portion of the full baking time.
Conveyor ovens are typically used in restaurant kitchens and commercial food manufacturing facilities. Typically they are kept running for extended periods of time, including periods when products are not being baked. Since the inlet and outlet ends of the oven are open, this means that heat and noise are continuously escaping from the conveyor oven tunnel into the surrounding environment. This escape of heat wastes energy. It also warms the surrounding environment, usually unnecessarily and often to uncomfortable levels. This is particularly the case where the conveyor oven is being used in relatively cramped restaurant kitchen environments. The escaping noise is also undesirable since it may interfere with interpersonal communication among those working near the oven.
Conventional conveyor ovens also provide users with limited ability to reduce energy losses while running at less than full capacity. Typically, users only have the ability to turn such ovens on or off, which in many cases involves an unacceptably long shut-down and/or start-up times. Therefore, it is necessary to leave such ovens on despite the waste of fuel or other energy supplied to the ovens when cooking food intermittently. It is not uncommon for a conventional conveyor oven to be left running in a full production mode for substantially the entire period of time a restaurant or other cooking facility is open.
It is generally desirable to maintain uniform heating from one end of the heated tunnel of the oven to the other. Among the challenges to be overcome in achieving such uniform heating are the inherent variations in heating from oven to oven due to variations in the internal physical environment of otherwise identical ovens. A more significant challenge to maintaining uniform heating through the length of the heated tunnel is the constantly changing physical and thermal configuration of the tunnel as food items being baked pass from one end of the tunnel to the other. For example, raw pizzas entering the inlet to the tunnel constantly change the physical and thermal configuration of the tunnel environment as they advance to the other end while drawing and emitting ever-varying amounts of heat. As a result, temperatures can vary by as much as 50-60° F. from one end of the tunnel to the other.
Currently, the most common technique for balancing the heating through the length of the tunnel involves monitoring temperatures near the inlet and outlet ends of the heated tunnel to maintain a predetermined average temperature over the length of the tunnel. Thus, for example, as a cold raw pizza enters the inlet to the tunnel causing a sudden drop in the tunnel temperature at the inlet, the drop in temperature is sensed and more heat is supplied to the tunnel to raise the temperature near the inlet heat sensor. Unfortunately, this also raises the temperature at the outlet of the oven, which causes the heat sensor at the outlet to trigger a heating reduction to prevent an excessive temperature at the oven outlet. In this way, temperature sensors near the inlet and outlet of the oven help to balance the heating of the tunnel to generally maintain a target average temperature.
However, uniform heating through the length of the heated tunnel cannot be achieved in this way. Thus, food items traveling through the oven do not see uniform heating which, it has been discovered, makes it necessary to slow the conveyor to a speed which completes the baking in more time than would be the case if uniform heating could be achieved throughout the length of the heated tunnel. In other words, improved heating uniformity from one end of the tunnel to the other may reduce required baking times.
Additionally, in many applications it is necessary to be able to operate the conveyor oven using either side as the inlet, by running the conveyor belt either from left-to-right for a left side inlet, or from right-to-left for a right side inlet. To be most successful in such interchangeable applications, it is particularly desirable to produce a uniform temperature from one end of the heated tunnel to the other.